RIO DE JANEIRO, Brazil — The skeleton of what is believed to be a new dinosaur species — a 105-foot plant-eater that is among the largest dinosaurs ever found — has been uncovered in Argentina, scientists said yesterday.

Scientists from Argentina and Brazil said the Patagonian dinosaur appears to represent a previously unknown species of Titanosaur because of the unique structure of its neck. They named it Futalognkosaurus dukei after the Mapuche Indian words for “giant” and “chief,” and for Duke Energy Argentina, which helped fund the skeleton’s excavation. “This is one of the biggest in the world and one of the most complete of these giants that exist,” said Jorge Calvo, director of the paleontology center at the National University of Comahue, Argentina. He was lead author of a study on the dinosaur published in the peer-reviewed Annals of the Brazilian Academy of Sciences.

Scientists said the giant herbivore walked the Earth some 88 million years ago, during the late Cretaceous period.

Since the first bones were found on the banks of Lake Barreales in the Argentine province of Neuquen in 2000, paleontologists have dug up the dinosaur’s neck, back region, hips, and the first vertebra of its tail.

“I’m pretty certain it’s a new species,” said Peter Mackovicky, associate curator for dinosaurs at Chicago’s Field Museum, who was not involved with the discovery. “I’ve seen some of the remains of Futalognkosaurus and it is truly gigantic.”

Mr. Calvo said the neck alone must have been 56 feet long, and by studying the vertebrae, they figured the tail probably measured 49 feet. The dinosaur reached over 43 feet tall, and the excavated spinal column weighed about 9 tons when excavated. One neck vertebra alone measured more than 3 feet high.

Jeff Wilson, an assistant professor of paleontology at the University of Michigan, who was asked to review the finding, said he was impressed by the sheer amount of skeleton recovered.

“I should really try to underscore how incredible it is to have partial skeleton of something this size,” Mr. Wilson said in telephone interview. “With these kind of bones you can’t study them by moving them around on the table; you have to move around them yourself.”

“It shows us the upper limit for dinosaur size,” Mr. Wilson added. “There are some that are bigger but they all top out around this size.”

Patagonia also was home to the other two largest dinosaur skeletons found to date — Argentinosaurus, at around 115 feet long, and Puertasaurus reuili, 115 feet to 131 feet long.

Comparison between the three herbivores, however, is difficult because scientists have only found few vertebrae of Puertasaurus, and while the skeleton of Futalognkosaurus (FOO-talong-koh-SOHR-us) is fairly complete, scientists have not uncovered any bones from its limbs.